Composite structures are structures consisting of two or more components often with some imparted order which are utilized in a wide variety of applications. For example, air vehicles, such as aircraft, spacecraft or the like, may utilize composite structures in order to take advantage of the benefits attributable to the increased strength-to-weight ratio offered by composite materials. Other applications that may include composite structures include other types of vehicles, such as automobiles, marine vehicles, bicycles and the like, as well as a wide variety of other structures, such as buildings, bridges, etc. Composite structures may also be produced and used with additional functionalities including altered thermal, electrical, acoustical, or mechanical properties by suitably modifying the materials used, the structure itself, or the process used to produce the structure.
Composite structures may be fabricated in various manners designed to impart a predetermined order to a plurality of elements dispersed within a resin or other mostly continuous medium, e.g, polymer, glass, or cement. Typically, a composite structure includes a plurality of structural fibers, such as glass fibers or other elements including carbon fibers, metalized carbon fibers, metal or polymer sheets, carbon or polymer veils, pre-impregnated composite sheets, woven sheets of fibers, matts of random or organized fibers, metal or polymer meshes, embedded in a resin matrix. The resin matrix may be any one of many thermoplastic or thermoset polymer combinations, adhesives or other bonding materials, or cement. Once the composite structure has been laid up, such as by placing a plurality of composite plies one upon another or by laying a plurality of composite tows one beside another, in a manner so as to have the desired shape or woven into a predetermined two dimensional (2D) or three dimensional (3D) structure, the composite structure may be cured, melted or bonded in one or more processing steps.
While composite structures offer a number of advantages, composite structures may occasionally have various anomalies, such as delamination between composite plies, waviness within the composite plies or marcelling in which a composite tow rolls at least partially on top of itself so as to create an inner swirl within the composite structure. While some of these anomalies may be detected from a visual inspection of the composite structure, a number of the anomalies may reside within the interior of the composite structure so as not to be detected during a visual inspection of the composite structure. As such, a variety of inspection techniques utilizing, for example, x-rays, ultrasonic signals or the like have been developed in order to interrogate the interior of a composite structure. While these inspection techniques may detect a number of anomalies, such as ply delaminations, other anomalies that may be created by the misorientation or misplacement of the structural fibers within the resin of a composite structure may present more of a challenge from a detection standpoint.
In this regard, the plurality of structural fibers or other elements within a composite structure generally extends in a predefined direction with the physical properties of the composite structure depending, at least in part, upon the directionality of the structural fibers or other elements. In some instances, however, the structural fibers or other elements within a composite structure may assume a different and an unintended orientation or position which may cause the physical properties of the composite structure to also be different. For example, the structural fibers or other included elements that extend proximate a resin-rich area may migrate or move toward or into the resin-rich area, thereby deviating from their intended orientation. The unintended orientation or position of the structural fibers may be the result of gravity, hydrostatic pressure, chemical or boiling action or mechanical action. Since this deviation in the orientation or position of the structural fibers or other elements may impact the physical properties of the composite structure, it would be desirable to detect such deviations in the orientation or position of the structural fibers or other elements as well as to detect other defects in the composite structure in a reliable manner such that appropriate repairs could be made, if so desired.